[Effect of plasmids on the multiplication indices of Escherichia coli]

The mechanisms of plasmid effect on multiplication of bacterial populations were studied. 22 different plasmids of antibiotic resistance, colicinogenicity and hemolytic activity were tested for their effect on the lag period and generation time of 1 smooth and 2 rough strains of E coli in comparison to the clonal structure of the respective plasmid variants with respect to the property of formation of rough mutants and in comparison to the molecular weight of the plasmids. There was a good agreement between the lag period, generation time, relative content of rough mutants in the population and molecular weights of the respective plasmids. It is suggested that the effect of the decreased intensity of bacterial population multiplication due to its infection with the plasmids is likely to be connected with accumulation of rough mutants having a lower multiplication rate.